The Daily Mail reports that 60 people were injured in the crush, which took place at the end of JLS's performance.
Fans surged forward to get a better look, causing a metal barrier to collapse. The event was cancelled, while ambulance crews set up a special unit to treat those who had been injured.
One woman suffered crush injuries to her pelvis, shoulder and leg, while another broke her ankle. Meanwhile, a teenage boy fractured his wrist and another teen suffered crush injuries to her back and leg.
"The remaining 56 patients suffered minor crush injuries and a range of minor medical complaints," an ambulance service spokesperson said. "They did not require further hospital treatment and were all discharged by ambulance crews at the scene."
Joan Durose, head of events at Birmingham City Council, said that the gates to the event were closed when 20,000 people had arrived.
"At the end of JLS's performance a security fence was breached, allowing too many people on to the square," she said. "We are very sorry that the event has had to be cancelled. We know that young people will be very disappointed, but the health and safety of thousands of young people at the event was our prime concern."
Tinchy Stryder, the Sugababes, Chipmunk, Little Boots, Alexandra Burke, the Noisettes and Pixie Lott had also been lined up to perform at the event.